Any theory of human mental evolution should, I think, strive to meet three criteria: evolutionary, psychological, and personal. The evolutionary criteria are paramount. Any theory of human mental evolution should play by the rules of evolutionary biology, using accepted principles of descent, variation, selection, genetics, and adaptation. It is best not to introduce speculative new processes of the sort that have been touted recently, such as "gene-culture co-evolution," "cognitive fluidity as a side-effect of having a large brain," or "quantum consciousness." Complex adaptations such as human mental capacities need to be explained by cumulative selection for a function that promotes survival or reproduction.
This evolutionary criterion makes it much more important to identify the selection pressures that shaped each adaptation than to identify how the adaptation went through some series of structural changes, having started from some primitive state. Complex adaptations are explained by identifying functional features and specifying their fitness costs and benefits in a biological context. The emphasis is on what and why, rather than how, when, or where. For every theory of every adaptation, there is one demand that modern biologists make: show me the fitness! That is, show how this trait promoted survival or reproduction.
Psychologically, the human mind as explained by the theory should bear some resemblance to the minds of ordinary women and men as we know them. The mental adaptations described in the theory should fit our understanding of normal human abilities and personalities. If you're married, imagine your in-laws. If you commute by public transport, visualize your traveling companions. They're the kinds of minds the theory should account for: ordinary people, in all their variation. We should not worry too much about the minds of exceptional geniuses such as theoretical physicists and management consultants. We are not really trying to explain "the human mind" as a single uniform trait, but human minds as collections of adaptations with details that vary according to age, sex, personality, culture, occupation, and so forth. Still, differences within our species are minor compared with differences across species, so it can be useful to analyze "the human mind" as distinct from "the chimpanzee mind" or "the mind of the blue-footed booby."
Finally, any theory of human origins should be satisfying at a personal level. It should give us insight into our own consciousness- It should seem as compelling in our rare moments of personal lucidity as it is when we are mired in that mixture of caffeine, television, habit, and self-delusion that in modern society we call "ordinary consciousness." It is so easy, when engaged in abstract theorizing about mental evolution, to forget that we are talking about the origins of our own genes, from our own parents, that built our own minds, over our own lifetime. Equally, we are talking about the origins of the genes that built the mind and body of the first person you ever fell in love with, and the last person, and everyone in between. A theory that can't give a satisfying account of your own mind, and the minds you've loved, will never be accepted as providing a scientific account of the other six billion human minds on this planet. Theories that don't fulfill this human hunger for self-explanation may win people's minds, but it will not win their hearts. The fact that 47 percent of Americans still think humans were created by God in the last ten thousand years suggests that evolutionary theories of human origins, however compelling at the rational level, have not proved satisfying to many people. We might as well admit that this is a third demand to impose on theories of human mental evolution, and see whether we can fulfill it. This criterion should not take precedence over evolutionary principles or psychological evidence, but I think it can be a useful guide in developing testable new ideas. If we cannot fulfill this criterion, perhaps we'll just have to live with the existential rootlessness that Jean-Paul Sartre viewed as an inevitable part of the human condition.
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